any atmospheric flow used to refer to the general circulation of the Earth and regional movements of air around areas of high and low pressure. On average, this circulation corresponds to large-scale wind systems arranged in several east-west belts that encircle the Earth. In the subtropical high-pressure belts near latitudes 30 N and 30 S (the horse latitudes), air descends and causes the trade winds to blow westward and equatorward at the Earth's surface. These merge and rise in the intertropical convergence zone near the Equator and blow eastward and poleward at altitudes of 2 to 17 km (1 to 11 miles). Part of the flow descends in the subtropical high-pressure belts, and the remainder merges at high altitudes with the midlatitude westerly winds farther poleward.
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